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Decadal scale signals in the Arctic's atmospheric and oceanic systems
Date: Wednesday, February 16, 2011 Time: 2:00 PM Location: 176 South Mudd, Caltech Speaker: Andrey Proshutinsky, WHOI
Arctic Climate Talk at Caltech
Significant changes in Arctic environmental conditions are evident. These changes include dramatic variations in sea-ice area, a substantial redistribution and thinning of sea ice, general increases in precipitation, glacier melt rates, and river discharge, rising sea level, alternating cyclonic and anticyclonic wind regimes with corresponding changes in ice drift and ocean circulation patterns, warming and increased areal extent of the Arctic Ocean's Atlantic layer and dramatic changes in the Arctic Ocean freshwater content. The conventional hypothesis for these changes is that they are regulated by the large-scale atmospheric circulation and can be described by the Arctic Oscillation (AO) index representing the leading mode of Northern Hemisphere sea level pressure (SLP) variability. However, the AO represents less than 20% of the winter time SLP change and frequently does not correlate well with changes in the central Arctic. An alternative index is an index of wind-driven circulation introduced by Proshutinsky and Johnson (1997): the Arctic Ocean Oscillation (AOO) index. Using this index, the wind-driven motion in the central Arctic can be characterized as anticyclonic during 1946-1952, 1958-1963, 1972-1979, 1984-1988, 1997-2008, 2010, while cyclonic motion dominated during 1953-1957, 1964-1971, 1980-1983, 1989-1996, and 2009. Shifts from one regime to another are forced by changes in the location and intensity of the Icelandic low and the Arctic high. Transformations from one regime to another occur quite rapidly and can be defined as climate shifts. The AOO index describes more than 35% of ocean variability and correlates better with the central Arctic environmental parameters than the AO index, although like the AO index, it cannot explain causes of decadal variability in the Arctic climate system.
Analyzing atmospheric, cryospheric, oceanic, and terrestrial time-series we have formulated a hypothesis along with supporting evidence that the anticyclonic Beaufort Gyre and the cyclonic Greenland Sea Gyre play a significant role in regulating Arctic climate variability. We demonstrate that the Beaufort Gyre accumulates a significant amount of fresh water during the anticyclonic circulation regime and releases this water to the Greenland Sea and North Atlantic during the cyclonic circulation regime. Depending on the circulation regime, the Greenland Sea Gyre regulates deep water formation and interactions of the Arctic with the North Atlantic. This hypothesis can explain the origin of the salinity anomalies periodically found in the North Atlantic as well as the role of freshwater and heat fluxes in the decadal variability in the Arctic region.